Hexagonal frame for the loop antenna receiver

Below are instructions for making a hexagonal frame for the loop antenna receiver. If you follow these directions you will have a nice looking single layer loop that will have no zigzags but a less carefully made frame will probably work just as well provided you maintain the dimensions fairly close.


The drawing above shows how the hexagonal frame is shaped slice a paddle wheel with the six’/4 inch plywood paddles mounted all facing in the same direction on the ends of three diagonals. The diagonals are 1″ X 2″ nominal, actual size 5/8″ X.1 3/8″, wood . Each diagonal is cut to be exactly 57 inches long. A hole is drilled in the centers of the three diagonals and they are fastened together with a bolt. We used 5/16-18 threaded brass rod and brass nuts and washers to prevent rust. The plywood paddles are 6-inches long and the width of 24 turns of whatever size wire. The paddle drawings show how the three countersunk holes for the mounting screws are centered on two paddles, offset 5/8″ to the right on two paddles and offset 5/8″ to the left on the other two. These offsets produce a hexagonal frame that will lay flat and the winding will not zigzag. We used #10 brass flat head wood screws 3/4″ long to mount the paddles on the diagonals. The paddies should extend exactly one inch beyond the ends of the 57 inch long diagonals so the distance between the ends is exactly 59 inches which is 1.5 meters.

When the diagonals are set with 30 degree angles between than the distance from each paddle to the next will be 0.75 meters and the length of a turn will be 6 X 0.75 = 4.5 meters. 24 turns will then require 4.5 X 24 = 108 meters or 354 feet of wire. This is a little more than the 300 feet usually recommended but it should work OK. Before we start to wind the wire on the

frame we clamp the diagonals so they won’t move. The center bolt cannot be made tight enough to do this. The wood for the diagonals comes in 8foot lengths so you will have some left over. We cut two pieces about 2-feet long to clamp the diagonals while winding the wire on the frame. Clamp these in place with C-clamps. We glue the finished winding to each paddle with 5-minute epoxy glue before removing the clamps. Now the diagonals can’t slip and the wire won’t slide off the edges of the paddles. The ends of the winding should pass through small holes both in the same paddle and extend out a few inches.

It was tuned by 1.5 meter loop with 24-turns of # 14 wires with a precision decade capacitor bank made by Cornell-Dubilier to determine the actual capacitances needed. Here are accurate values for the capacitors needed to tune to some popular VLF stations.

60 kHz, WWVB Fort Coffins, Colorado, USA. ……0.002 mfd
25.2 kHz La Mourie, North Dakota, USA …0.0175 mfd
NAA 24 kHz Cutler, Maine, USA ……0.0185 mfd
37.5 kHz, NRK Grindavik Iceland ……0.008 mfd
24.8 kHz, Tim Creek, WA, USA …….. 0.0178 mfd
21.4 kHz, NPM Hawaii, USA……….. 0.023 mfd

We can make a tuner to find these stations from two Radio Shack 8-position DIP switches. These consist of eight little single pole, single-throw switches side by side that mount on a Printed Circuit Board. Radio Shack only carries the capacitors we need for this tuner in ceramic dielectric so you should use their ceramic capacitors. Below are the capacitances for the sixteen capacitors we will need. Mount each switch on a little circuit board and connect the capacitor to each switch so when all 8 switches are in the an position all eight capacitors are connected in parallel.

*      Switch Number One:
Position # 1…..100 pfd
            2…..100 pfd
            3…..100 pfd
            4…..100 pfd
            5…..100 pfd
            6…..470 pfd
            7…..470 pfd

*      Switch Number Two:
Position # 1…0.001 mfd
            2…0.001 mfd
            3…0.001 mfd
            4…0.0047 mfd
            5…0.0047 mfd
            6….0.01 mfd
            7….0.01 mfd
            8….0.01 mfd

These two tuners should make it possible to find the station without an oscilloscope and signal generator. We connect them temporarily with Alligator clip leads across the Loop. Then tune up and down in 100 pfd increments until we peak on a strong signal. We used a multimeter or our recorder to measure signal strength. We recorded the strong signal found for a few days to make sure it shows sunrise and sunset patterns. If it shows these patterns we have successfully tuned our receiver to a suitable signal and it should record solar flares as SESs. We unsolder the selected capacitors from the tuners and solder them across the ends of the loop. The ceramic capacitors are rated for only 20% accuracy so we connect the values in the table above to our loop. We connected 20% capacitors adding up to 0.185 mfd across the loop.